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870

small tubes made of sand
Yesterday we found several large areas that were covered with these tiny tubes. Each is about the diameter of a drinking straw. What caused this?

Answer:

Science photo 870

These are nesting tubes for cactus bees. These bees are solitary, which means that each one has its own tube, but they are communal, which means that they build their tubes close to each other. Cactus bees mainly pollinate cactus, and lay their eggs when most of the cactus are in bloom.

I was surprised at how firmly the sand was cemented into the tubes, and how perfectly round they were. In spite of their small size, the bees zipped in and out of the holes so fast that it was difficult to photograph them.

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